One of the leading complications of cardiovascular disease is a condition known as atherosclerosis in which the arteries harden from fibrosis or calcification and/or narrow due to plaque formation within the arterial lumen. Patients who suffer from atherosclerosis are susceptible to developing aneurysms in certain regions of the body. These aneurysms, which are enlargements of the blood vessel caused by a weakening of the vessel wall, can often occur in areas such as the ascending aorta, aortic arch, thoracic aorta, or abdominal aorta. If left untreated, the aneurysm can grow and potentially rupture, causing massive hemorrhaging resulting in death.
Current modes for aneurysm repair require surgical intervention and frequently involve bypass grafting procedures. In a traditional aortic aneurysm repair, direct surgical access to the aneurysm is gained, after which the diseased portion of the vessel is excised and replaced with a prosthetic graft that is anastomosed, or reattached, to the healthy remainder of the aorta. Gaining in popularity is a minimally invasive technique whereby a sutureless vascular graft placed within the abdominal aorta spans the length of the aneurysm and provides a new pathway for blood flow through the diseased region of the vessel. In patients who are candidates for this minimally invasive procedure, a guidewire is introduced into the femoral artery after surgical exposure of the artery. Using fluoroscopic guidance, a catheter delivery system can be inserted over the guidewire and positioned across the aneurysm. Once the catheter is in place, a vascular prosthesis such as a compressed graft with self-expanding barbs at each end can be released at the diseased region. The barbs anchor the graft to the walls of the vessel, creating a circumferential seal at locations above and below the aneurysm to isolate the aneurysmal wall from intraluminal blood flow and pressure, thereby preventing further expansion of the aneurysm and decreasing the risk of rupture. Finally, the delivery catheter is removed, leaving the deployed prosthesis.
In both surgical procedures described above, branches which arise from the aneurysmal section of the involved artery are routinely excluded from the patient's circulation in order to adequately replace the weakened artery. When such branches are small or provide flow to tissues which have alternative blood supply from an artery arising from a region remote to the aneurysm, they can be sacrificed without complication. On the other hand, if the branches which arise from the aneurysm are critical to the normal function of vital organs, they must be protected during exclusion of the aneurysm and then restored to circulation by surgical reimplantation into the prosthetic graft. In the minimally invasive surgical method, there is at present no technique for protection and restoration of important branches which arise directly from the aneurysmal region of the aorta. Consequently, the presence of an important branch within the aneurysm is one of the criteria which can disqualify a patient from being a candidate for this minimally invasive surgery.
In the traditional surgical method, the aneurysmal section of the artery is temporarily clamped to stop flow in order to provide a blood-free field for the surgeon to operate. This clamping necessarily cuts off blood flow to vessels that branch from the clamped artery. When flow to the branch vessels cannot be preserved during clamping or restored promptly, damage to the tissue that rely on these branched vessels is likely. For example, one of the most devastating complications affecting about 10-15 percent of patients undergoing surgery to repair extensive aneurysms involving the thoracic and abdominal aorta together is paraparesis or paraplegia, a weakening or paralysis of the lower extremities caused by the temporary or permanent interruption of blood flow through small branches supplying the spinal cord. In this situation, arterial clamping prevents the thoracic intercostal arteries from feeding blood to the anterior spinal artery and adequate spinal blood flow must be derived from collateral arteries arising from other sources. Measures to protect the spinal cord from injury during clamping and prior to surgical reimplantation into the prosthetic graft include anticoagulation, use of a temporary aortic bypass or shunt, and neural protection using pharmacological agents, topical or systemic cooling, and spinal fluid drainage. All of these measures have proven helpful, but the risk of spinal cord injury has yet to be completely eliminated.
Moreover, there is an irreducible minority of patients who appear to be absolutely dependent on continuous blood flow to the spinal cord by way of the intercostal arteries. These individuals appear to require near-continuous temporary perfusion of the intercostal arteries during aortic clamping, followed by subsequent reimplantation of the intercostal arteries into the prosthetic graft, to avoid spinal ischemia. The chief impediment to this strategy has thus far been the lack of a reliable and satisfactory technique for the temporary perfusion of the intercostal arteries.
Currently available devices for temporary perfusion of the intercostal arteries require direct cannulation of these small vessels, which are typically 1-2 mm in diameter. Direct cannulation can be unwieldy and cumbersome, often producing inadequate sealing between the cannula and the vessel which results in poor flow into the vessel and a high likelihood of permanent vessel damage. There is thus a need for a new perfusion device that is designed to solve the problem of safely and effectively interfacing with small branch vessels such as the intercostal arteries. Specifically, there is a need for a perfusion catheter that allows adequate continuous selective temporary blood flow to small vascular branches during aortic clamping without causing injury to the vessels themselves.